In small, fractional and subfractional horsepower, permanent magnet direct current motors, brush gear and a commutator are typically used to transfer electrical power from motor terminals to rotor windings. The commutator, which consists of copper segments laid on a commutator base, is located adjacent one of the bearings rotationally supporting the rotor. Such bearings are typically oil impregnated sintered bushings due to wear and cost considerations. One disadvantage of these bearings is that the oil is not sealed within the bushing and tends to migrate along the shaft. Such migration, if not checked, can extend to the commutator segments where the oil contaminates the brush/segment interface and mixes with brush dust ultimately rendering the motor inoperable by short circuiting commutator segments. Carbon brushes are hydroscopic and readily soak up oil. The brushes then become abrasive and quickly grind down the commutator segments. Oil migration is also a problem for ball and roller bearings, albeit not as great, especially in high temperature applications such as within the engine compartment of a vehicle.
In motors used over a wide range of temperatures, for example, the motors used in the engine compartment of a motor vehicle, such as the electronic throttle control motor, the motor for adjusting the vane angle in a turbocharger or supercharger, suction intake pipe actuator, swirl actuator, air flaps, and bypass flaps, etc, which must operate satisfactorily over a wide ambient temperature range, for example, from −40° C. to 180° C., the management of oil in the sintered oil impregnated bushings becomes problematic due to a difference in the coefficient of thermal expansion of the lubricating oil and the material of the bushings. Typical lubricating oils used in sintered bushings have a coefficient of thermal expansion between 2.2 to 3.4×10−4, whereas typical sintered bushings have a coefficient of thermal expansion between 12 to 18×10−6. At 180° C., the oil volume expands far greater than the volume for the oil in the bushing resulting in oil being pushed out of the bushing. Some of this oil migrates along the shaft. For the bushing at the commutator end of the motor, this oil migration causes a serious life issue. Should the migrating oil reach the commutator and contaminate the commutator segments, the motor will fail.
In the past slingers have been used to fling the migrating oil from the shaft on to the surrounding motor casing. The slinger looks like a washer fixed to the shaft. See, for example, GB2207956. However, this results in loss of oil and when the motor is then asked to operate in a low-temperature situation, e.g. at startup after a night in snow country, the oil volume which has been already reduced due to the loss of oil is now further reduced due to the thermal contraction. Thus resulting in the bushing running dry at the beginning, possibly producing an annoying squeaking noise. However, the squeaking noise is indicating a period of high metal on metal wear occurring at the shaft/bearing interface.
Also, in the modern engine compartment, these motors are often operated through a very limited range of motion and are expected to work first time, every time. By limited range of motion, typically less than 20 revolutions, maximum, in any one direction, which often is not enough to warm up the bearing oil enough to establish a hydraulic lubricating oil film. Indeed, some motors operate for just a few milli-seconds or less than one complete revolution. In such situations, the use of the standard oil slinger is not helpful as the oil is not slung off, and merely delays migration of the oil to the commutator but does not stop the oil.
GB2192312 address this problem by providing a rubber oil collector disc which traps the oil. However, being rubber, care and space is required to prevent the disc from coming into direct contact with the bearing. Also, the motor is not suitable for use in very high temperature applications. It is also not suitable for use in motors subjected to high vibration operating conditions. In addition, there may be problems associated with a possible chemical reaction between the oil and the rubber, out gassing of the rubber and the breakdown or aging of the rubber material over time.
Hence, there is a desire or need for a oil collector, which is more suitable for use over a wide temperature range.
There is also a secondary desire for such an improved oil collector, which can return collected oil to the bushing thereby creating an oil recirculating system. Thus retaining a high percentage of the oil.